Special Issue on NEC's Smart Energy Solutions Led by ICT
Solutions for energy enterprises
Grid Stabilization Solution That Helps Ensure a
Stable Supply of Electric Power: Grid Energy Storage
System for Italy’s ENEL
FUJITA Yoshikazu
Abstract
In sunny southern Italy, energy production from renewable sources such as solar and wind power has been
growing rapidly. As these forms of energy can be difficult to deliver consistently, ensuring stabilized operation
of electric grids that use these sources is now a big issue. Italy’s largest distribution system operator, ENEL Distribuzione sees the energy storage system as one of the most promising solutions for the stabilization of electric
grids accompanied by the massive introduction of renewable energy. To help ENEL prepare for full deployment
of the energy storage, NEC implemented a demonstration system in the field. The energy storage system for
electric grids installed by NEC at an ENEL substation in southern Italy has been highly evaluated in terms of both
performance and quality.
Keywords
lithium-ion battery, power storage system, system stabilization
1. Introduction
A wind farm that exploits the characteristics of a valley that acts as a natural wind tunnel
The European Union (EU) has declared the targets of
reducing greenhouse gas emissions by 20% compared
to 1990 as well as increasing the ratio of renewable energy in total energy consumption by 20% and improving energy efficiency by 20% by 2020 as the measures
against climate change. Italy is no exception in making
efforts to promote the introduction of renewable energy based on the EU’s targets. Among the country’s
efforts, solar and wind power generation has been massively popularized in southern Italy due to the region’s
geographical and environmental factors - such as the
amount of sunshine and the type of wind conditions -
Mega-solar panels that take advantage of
southern Italy’s high percentage of sunshine
Many wind farms are
located in this valley where
the local geographical
features ensure smooth,
consistent wind flow
Chiaravalle Centrale
substation
Mega Solar panels
Mega Solar panels
Fig. 1 Renewable energy in southern Italy.
which make it ideal for renewable energy production
(Fig. 1).
ENEL Distribuzione (hereinafter referred to as ENEL),
stalled by NEC in the Calabria region of southern Italy in
Italy’s largest power distribution system operator, is
2014, which is now being used for stabilization valida-
investigating the introduction of large scale energy stor-
tion tests of ENEL’s power distribution systems.
age system as a means of stabilizing a power system
undergoing a massive introduction of renewable energy.
In this paper, we will look at one of the most promising
solutions of this type, a grid energy storage system in-
2. Issues of System Stabilization in Southern Italy
Headquartered in Rome, ENEL is Italy’s largest elec-
NEC Technical Journal／Vol.10 No.2／Special Issue on NEC's Smart Energy Solutions Led by ICT
75
Solutions for energy enterprises
Grid Stabilization Solution That Helps Ensure a Stable Supply of Electric Power: Grid Energy Storage System for Italy’s ENEL
tric power company and operates about 85% of the do-
NEC’s grid energy storage system was installed at the
mestic distribution network. As it moves to increase the
Chiaravalle Centrale substation. To ensure a stable sup-
amount of power generated using renewables in order to
ply of high-quality power, it incorporates the following
meet the EU’s energy targets, ENEL has faced a number
functions.
of challenges.
(1) Balancing control between supply and demand
The primary problem is that renewable energy sourc-
As mentioned above, the amount of energy pro-
es are highly dependent on the weather. Intermittent
duced by renewables such as solar and wind fluc-
wind or cloudy skies can significantly reduce the energy
tuates depending on the level of sunshine and wind
produced from these sources, which makes it difficult to
conditions. This makes it difficult to forecast gen-
forecast the amount of electricity that will be generated.
erated power and prepare a generation plan in ad-
When a power grid draws a large amount of power from
vance. To maintain the frequency of an electric pow-
renewable energy sources, it becomes more difficult to
er grid, supply and demand need to be coordinated
adjust supply to meet demand in real time and to keep
with each other at all times. An energy storage sys-
the power frequency within the specified range.
tem is used to fill the gap created by the errors in
Recently, we have seen renewable energy being fre-
the planned and actual values of a supply-demand
quently connected to downstream substations. This
balance. ENEL’s operation center monitors actual
has caused voltages in many of the major substations
demand and supply and, when an error occurs be-
to increase and created reverse power flows from me-
tween the planned and actual values, sends com-
dium-voltage cables to high-voltage cables. This can
mands to the storage system to charge or discharge
result in unexpected generation of electric currents, producing instability in the power transmission and causing
the quality of power to deteriorate.
as necessary in order to correct the error.
(2) Frequency regulation
As described in (1) above, controlling the sup-
The Chiaravalle Centrale substation (Calabria, Italy),
ply-demand balance based on commands from the
where NEC installed the grid energy storage system, has
power supply command center is effective in cor-
a huge number of solar and wind systems connected to
recting the imbalance for longer time cycles from
its distribution networks. Dues to the high percentage
less than an hour to a few hours. However, the
of sunshine, the power generated by renewables in this
response times of communication networks and
region often exceeds - more often than the year before
systems mean that it is not effective when dealing
- the total demand from the substation’s coverage area.
with shorter time cycles from a few seconds to a
This has caused unexpected reverse power flows to the
few minutes. The energy storage system monitors
distribution networks, resulting in unstable power trans-
power system frequency 24/7, compensating for
mission and poor power quality.
any deviations from the specified range by autonomously charging and discharging according to the
3. Grid Energy Storage System
degree of deviation.
(3) Voltage regulation
To solve the problem of ensuring a stable power grid
In the same way as it does with the frequency reg-
when large amounts of renewable energy are incorpo-
ulation function, the energy storage system always
rated in the system, ENEL chose NEC. A grid energy
monitors the voltage of the power system. When
storage system (Photo) was installed that uses lithi-
the voltage deviates from the specified range, it au-
um-ion batteries capable of storing 2-MWh power and
tonomously controls reactive power according to the
validation tests were conducted to see how effective this
storage system was at stabilizing the grid.
degree of deviation and compensates the voltage.
(4) Backup power supplies in the event of a blackout
Backup power supplies are supplied to critical facilities such as hospitals, police stations, and factories
whenever a blackout occurs. Even if the auxiliary
power unit goes down, the energy storage system
can continue to supply power to critical facilities while
powering itself using its own lithium-ion batteries.
(5) Power quality compensation functions
To maintain the quality of power, the energy stor-
Photo View of the grid storage system.
76
age function has a voltage compensation function
NEC Technical Journal／Vol.10 No.2／Special Issue on NEC's Smart Energy Solutions Led by ICT
Solutions for energy enterprises
Grid Stabilization Solution That Helps Ensure a Stable Supply of Electric Power: Grid Energy Storage System for Italy’s ENEL
that compensates for any sudden drop in voltage by
supplying effective power, as well as a function that
suppresses higher harmonic waves mixed in the
power system.
In the validation tests for ENEL as described above, we
have verified the technological effectiveness of the system’s ability to supply power when a momentary voltage
drop or even blackout occurs, as well as to stabilize the
frequency and voltage within the specified ranges.
4. Conclusion
As a key component of strategies to reduce greenhouse gas emissions, renewable energy is of growing
importance not only for Europe but for the whole world.
Increasing the effectiveness and reliability of renewable
energy, as well as improving the operation capability of
power transmission networks connected to significant
renewable energy sources, is becoming more and more
critical.
ENEL’s comprehensive testing of NEC’s grid energy
storage system resulted in a high evaluation of our technological expertise and project management capability,
as well as the high-level performance and quality of our
systems.
ENEL is looking forward to the achievement of flexible power networks in which conventional energy and
renewable energy coexist by using our ICT and energy
storage system. As a world leader in both ICT and electricity storage technologies, NEC will continue to contribute to the construction of new power networks centering
around renewable energy.
Authors’ Profiles
FUJITA Yoshikazu
Manager
Solution Department
1st Smart Energy Division
NEC Technical Journal／Vol.10 No.2／Special Issue on NEC's Smart Energy Solutions Led by ICT
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